Method of reducing iron oxide to sponge iron



H. FREEMAN 2,855,290

METHOD OF REOUOING IRON OXIDE TO sPoNGE: IRON Oct. 7, 1958 2Sheets-Sheen'.l 1

Filed July 12, 1956 kbbug mnnmddml zokNH mmlr mutkokh. Luqqul IN VEN TORHo RA cg fe-EMA N.

BY Mwahm/Mmm ATTORNEYS.

Oct. 7, 1958 H. FREEMAN METHOD oF REDUCING IRON-@MDE To sPoNGE IRONFiled July 12, 195e 2 Sheets-Sheet 2 nited States Patent METHOD OFREDUCING IRON OXIDE TO SPONGE IRON Horace Freeman, Cap-de-la-Madelene,Quebec, Canada, assignor to Freeman Corporation, Cap-de-la-Madelene,Quebec, Canada, a corporation of Canada Application July 12, 1956,Serial No. 597,507

Claims priority, application Canada April 4, 1956 11 Claims. (Cl. 75-33)This invention relates to a process for directly reducing metal oxides,especially the oxides of iron, cobalt, nickel and copper to the spongemetal state. More particularly, the invention relates to reduction ofiron oxide pellets to sponge iron by the action of carbon monoxide. Inanother aspect, the present invention relates to the production of alime-containing powder simultaneously with the production of spongemetal, which when separated from the iron is suitable for use in themanufacture of cement. In order to simplify its description, the processwill be described herein as applied to iron oxide and the production ofsponge iron, however, it is to be understood that the process islikewise effective to reduce the oxides of copper, cobalt and nickel.

v Heretofore, efforts to continuously and directly reduce iron oxide tosponge iron or the like in rotary kilns or other reduction furnaces haveinvolved the countercurrent flow of hot gases which frequently causessintering of the already hot reduced iron causing the same to lump andstick `to the sides of the furnace at its discharge end. Previousfurnace operations, and particularly the blast furnace which is a spongeiron producer, have involved excessive expenses for fuel, and theresulting product contains appreciable amounts of oxide, ash and carbonwhich is employed to produce the reducing agent carbon monoxide. lnaddition, the blast furnace requires a hard, expensive, low sulfur coketo the extent of nearly one ton (requiring about two tons of coal) foreach ton of iron produced with the aid of about half a ton of limestone.The main shortcoming of the blast furnace lies in its thermalinefficiency, often less than 50 percent, which is derived from the factthat the reducing agent, carbon monoxide, is present in concentrationsof only about 25 percent by volume. At this low concentration it mustdiffuse into and out of large lumps of ore, necessitating a period ofreduction to sponge iron in the upper part of the furnace ofapproximately eight hours.

The present invention, on the other hand, provides a method ofovercoming the above enumerated diliiculties encountered in blastfurnace operations, a method which is more economical, and one whichprovides a high concentration of carbon monoxide in intimate contactwith the oxide pellets. The present process makes possible the directand complete reduction of iron oxide to sponge iron which may containless than 0.03 percent carbon.

In my copending U. S. patent application Serial No. 422,187, filed April9, i954, now U. S. Patent 2,792,298, of which the present application isa continuation-impart, I described a method of reducing iron oxidepellets to sponge iron by feeding such pellets together with finelydivided carbon of a nature such that its ash does not fuse or sinter atthe reaction temperature or" l9002100 F. into a rotary kiln or othersuitable furnace together with a limited quantity of air sufficient tooxidize the carbon to carbon monoxide, which in turn reduces the iron.In that process, excess carbon is employed over that required in orderto convert the carbon dioxide formed during ,reduction of the iron oxideto carbon monoxide, thus y 2,855,290 Patented Oct. 7, 1958 maintaining areducing atmosphere with respect to the hot iron pellets. While thepresent invention departs from the teachings of my earlier applicationin many respects, the principle difference resides in the use ofconsiderably less carbon, carbon monoxide being produced by the actionof carbon upon carbon dioxide produced by Ithe decomposition oflimestone.

Briefly, the present invention involves first grinding the iron oxide toa powder and then forming the same into small, hard, porous pellets,which are preferably then roasted in air to remove sulfur and furtherharden the pellets. The pellets are fed to a rotary kiln along with afinely divided reducing agent comprising a solid carbonaceous materialand limestone or calcium carbonate. The carbonaceous material isdesirably such that its ash does not fuse or sinter at the reactiontemperature in the kiln or furnace. However, this is not essential sincecalcium carbonate is present in amounts sufficient to raise the fusionpoint of the ash so that it is several hundred degrees above thetemperature within the furnace. Air is admitted to the charging end ofthe kiln where there is located a fuel oil or gas flame which raises thetemperature of the charge to about 900-l000 C., at which temperature thefinely divided limestone therein decomposes forming vcalcium oxide andcarbon dioxide. The carbon dioxide in the presence of hot carbon israpidly reduced to carbon monoxide, thus providing a very high monoxideconcentration within the charge in intimate contact with the iron oxidepellets, which reduces them to metallic iron. The charge together withthe atmosphere above it are advanced co-currently through the kiln, theformer through inclination and rotation of the kiln and the latter byinduced draft. The calcium oxide thus produced substantially completelyabsorbs sulfur present in the carbonaceous material. The sponge iron inpellet form issuing from the discharge end of the furnace is suitablycooled in an atmosphere which is non-oxidizing with respect to the hotiron. The pellets are readily separated from the finely divided lime,ash, and any excess solid carbonaceous material present by screening, bymagnetic separation, or by a novel air separation described hereinafter.The finely divided material is suitable for calcining to cement, in someinstances Without the addition of other material, and the presentinvention contemplates cement manufacture from this material.

The decomposition of limestone to lime and carbon dioxide:

CaCO8=CaO+CO2 1 conversion of the dioxide to monoxide by carbon:

CO2'-|-C=2CO (2) as well as the reaction in the presence of hot carbonbetween lime and sulfur impurities:

are all endothermic reactions which take place simultaneously. The ratesof reaction become appreciable at 900 C. and quite rapid at 1000 C., thetemperatures at which the iron oxide reduction is preferably conducted.The reduction reaction, on the other hand, is exothermic as indicated bythe following equation:

Fe2O3+3CO=2Fe+3CO (4) +300 B. t. u. per pound of Fe produced paratus;

Fig. 2 is a schematic view of the rotating kiln reducing furnace of Fig.1, together with its associated' cooling zone, illustrating conditionswithin the kiln; and

Fig. 3 is a schematic diagram of preferred apparatus in which thesponge. metal pellets are separated from the powdered lime ash, and'simultaneously cleaned.

Preparation of iron` oxide The iron oxide to be reduced may be in anywellknown form, such as magnetite, its industrialcounterpart rollingmill scale, or it may comprise iron oxide cinder resulting from thecombustion of ironsulfde ores. Such cinder is presentlyavailable atlowcost: in large quantities, and despite its sulfur content, it. may beeconomically used in carrying out the present. invention. The oxide mayor may not contain appreciable quantities of nonferrous material, suchas silica gangue, without unduly` interfering with the process, exceptit shouldv be understood that if sponge iron of exceptional purity isrequired, a highly pure oxide or ore such as Brazilian lietnatit'eshould be used.

Since reduction of the oxide iseffected by carbon monoxide and bydiffusion and absorption ofthis gas into pieces ofthe oxide and ofthegaseous products outward, the advantages of using as small pieces ofoxide as practicable and of having; these pieces as nearly as possiblethe same size are obvious. Thus, the iron oxide used is rst finelydivided, either in wet or dry condition, in a grinder 10,. such as aball mill, to a degree. of neness required for forming pellets, suchneness, however, not being particularly critical. It. is preferable toadd a binding material during grinding if the oxide is dry ground, orafter grinding if it is done wet. Various binders'may be used, with anorganic material leaving no residue being preferred for use i-npreparing highgrade sponge iron for iron powder, but cheaper inorganicbinders are adequate for melting stock production. Generally speaking,the binding materialmay comprise ordinary wheat our, molasses, sodiumsilicate, suliite liquor, lime, caustic soda, or mcagnesia, any of whichused-inthe order of 0.5 to 2 percent by weight of the ore will give asufiiciently hard pellet without adversely affecting the purity of theproduct. Where highpurity of theiron product is required, a bindershould be used which will yield as little as possible in the way ofimpurities upon heating.

The thus ground iron oxide and, binder'are then thoroughly mixed orblendedtasin a pug-mill 11 with about 1.0. percent` lby weightof. watcr,or after` de -wateringl to percent moisture if the ore was wet ground.The blended material is then shaped orextruded as at 12, preferably instandard extrusion equipment such as that used in the; clay'industry,into smallspherical or short' cylindrical masses. The'darnp` extrusionsare then fed to a rotating drum indicatedl pellenzer 13which may besimilar'in construction tpg that` off an ordinary rotating roastingkiln. The small" shaped or' extruded masses become rounded approximatelyinto-spheres by the rolling action as. they pass through pelletizer Y13,and they are driedand hardened through Contact withhot gases enteringthe pelletizer at 14 flowing countercurrently tofthe bed of pelletstherein, and being exhausted'through stack 1S at the charging end of thepelleti'zerto the'atrnosphere. Pelletizer 13 is rotated slowly so, as topievent breakage of the pellets being dried thereby avoiding theformation of iron oxide lines which cause sintering in the subsequentreduction operation'. However, rotation is suicient to permitsubstantially complete drying of the oxide masses.

or 2" or more in diameter. Size of the' pellets may'be' controlled byregulating the moisture content of' theV blend being shapedor extruded.For best' results, andrapid.

reduction later in Vthe process, pellet' diameters between about 1A" and3A, e. g. j/z", are preferred. In any case, the pellets should besufficiently larger than the limestone and carbonaceous material whichare mixed therewith later, so that the latter may serve as a neinterfering phase preventing agglomeration of pellets during reduction,and so that the reduced pellets may be cleanly separated from the lime,ash and carbon, if any, issuing from the reduction furnace.

While the thus formed iron oxide pellets are generally sufficiently*hard to resist attrition in subsequent reducing and handling operationsand may be reduced directly, l have found that roasting in some casesnot only improves pellet hardness and removes sulfur but alsosubstantially completely converts the oxide to Fe203 thus facilitatingreduction tol iron. Accordingly, I prefer to roastthe pellets in air.They, areV conveyed, preferably pneumatically, to a moving bed or shaftroaster illustrated at 15.` If the ore be magnetite, i. e., ferrousoxide, roasting may be eiected'without the addition of fuel to theroaster charge under proper conditions, since conversion of ferrous toferrie iron is accomplished by the generation of heat suliicient tobring the pellets to incipient fusion at aV temperature in theneighborhood of 1500 C. The reaction isA as follows:

Roasting is carried out by blowing air through aV column or bed ofpellets in roaster l5 after the same have been ignited by an externalsource of heat. lf the column orl bed of pellets is kept in motion as bycontinuous feed and discharge, there will be no sticking. Cooling'may beelfccted at the base of the roaster' by incoming air. The roastedpellets will be substantially sulfur-free, gamma hematite, extremelyhard, porous, somewhat vitreous yet completely permeable to the reducinggases. They completely resist abrasion in the presence of the finelydivided limestone and carbonaceous material dur-4 ing the reductionprocess.

It will be obvious that if hematite or ferrie oxide be the ore used itis not capable of further oxidation and the' pellets thereof will not beself-roasting, but it has been found that if approximately 7 percent ofits weight of the reduced metallic iron powder be added to this type of'ore in the grinding operation, it will yield a mixture behaving for theprocess of this invention as if it were the ferrous or magnetic oxideand is then self-roasting.

Y lternatively, approximately one and one half percent byl weight ofcarbon in the form of coke may be addedl during grinding of thehematite. enough heat, during roasting, to bring the pellets to'incipient fusion. d

Either thev dried pellets or dried and roasted pellets,k if they havebeen prepared with a binder such as flour or molasses, free from suchmetallic bases as soda, lime' or magnesia, will, upon reduction to iron,swell considerably, giving pellets of sponge iron twice as large orlarger than the original oxide pellet `and though this isadvantageousfor some uses, as when a very tine, light, porous ironpowder is required, it is undesirable for other uses where largerparticle size and higher'density is required. This swelling may beentirely prevented by using one half of one percent by weight of theore, either ofl soda, lime or magnesia as a binding agent in thepelleting operation, witlror without the. use of organic binders. Thesebases are found to combine with the iron oxidev in the high temperatureselflroasting operation with the result, that, in later reduction thepellets do not swell and may be comminuted to give a dense metallicpowder of large particle size, due no doubt to the bonds eifectedf bythe fused base addition.

The reduci/1g agent While' the compound relied upon to actually reduce.the iron oxide pellets to iron is carbon monoxide, thev This suiiices toproduce' mixture relied upon to initially produce this gas is termed thereducing agent herein. It comprises a nely divided mixture of limestoneand solid carbonaceous material. In former processes for the reductionof the oxide to sponge iron carbon has been employed as the primarysource of carbon monoxide, with the carbon being oxidized only to themonoxide in an oxygen deficient atmosphere as follows:

with reduction of ferric oxide proceeding in accordance with Equation 4.It will be observed that for each mole of Fe203 reduced, three moles ofCO are required, which require, according to Equation 6, three moles ofC, neglecting of course additional carbon required to reduce the CO2produced in the ore reduction. Accordingly, a process requiring lesscarbon such as that of the present invention would be veconomicallyattractive.

Drawing Iattention to Equation 2, it will be seen that two moles of COmay be produced from but one mole of C when the material being reducedis CO2. Thus instead of three moles of carbon, only one and one-halfmoles are required to effect the reduction of Equation 4. The economicsaving is not one-half as may be supposed, since the heat liberated bycombustion of carbon to carbon monoxide `and required to raise thetemperature of the ore must now be supplied in part from another source.This source is desirably fuel oil, natural or coke oven gas Which areconsiderably cheaper in most localities than carbon in the form of highgrade coke which is employed for the most part today.

The carbonaceous material employed in the present process is desirablycoke or anthracite. However, the coke may be a low grade material, forexample, high in sulfur content such as that produced from Nova Scotiabituminous coal which contains about 3 percent sulfur originally. Sulfurintroduced from the coke or anthracite during reduction is substantiallycompletely scavenged in accordance with Equation 3 and does not appearin the iron product. In view of the high concentration of limestone andlime with respect to ash present during reduction, fusion of the ash ofthe carbonaceous material is no longer a limiting factor. The fusiontemperature of the ash of the above Nova Scotia bituminous is only about1050-1 100 C., temperatures which, although not necessary, might easilybe reached during reduction in accordance with the present invention.However, due to the presence of limestone and lime the fusion point ofthe ash is raised approximately 200 C.

Although coke and anthracite are preferred, the process has been carriedout successfully with the raw Nova Scotia bituminous, and the presentinvention contemplates the use of uncoked soft coal. When such amaterial is employed, the volatiles therein, usually constituting aboutone-third by weight of the coal, are burned in the reducing zone therebyproviding heat for the reduction and greatly reducing gas or fuel oilrequirements. However, coking of the coal within the reducing zone mustbe avoided since the tine particles tend to agglomerate and stick to thepellets. This necessitates critical temperature control within thereducing furnace. Thus, While bituminous coal may be employed,anthracite or coke are preferred, with coke being the more reactive. Inpresent operation of the process, the low grade soft coal is utilized ona coking stoker from which the volatiles are used to replace oil inproviding the heat required in the reducing furnace, and the coketherefrom is employed in the reducing agent.

The limestone is conveniently a low grade shaly stone containing about80 percent CaCO3, preferably of cement making composition which may beused for cement production after its use in the reduction. In someinstances the magnesia, alumina and silica present in coal or coke ashwill supplement these metal oxides in the limestone to the properdegree, in which case the finely divided material separated from theiron pellets at the end of the process may be calcined directly tocement. For example, a composition known to be entirely satisfactorywhen applied to a wide variety of cementitious raw materials is:

Caco3 required=4-1sio2+2-6n2o3 l(7) by weight, where R203 refers toiron, magnesium, aluminum and other metal oxides. Preferably, however,the composition of the lime and unreduced metal oxide powder separatednom the pellets will be adjusted in accordance with the above generalformula and then calcined to cement. Thus while virtually any limestonewill suftice as a component of the reducing agent mixture, a shalycement-forming stone is preferred since obvious economic advantagesaccrue where the powder is calcined to cement.

During reduction the limestone not only serves as a source of carbondioxide and makes possible the effective absorption of sulfur from thecoke and prevents its entry into the iron pellets, but it also raisesthe fusion point of the coke ash as noted earlier. Furthermore, thelimestone and lime produced therefrom acts as an infusible interferingphase between the pellets thereby preventing the metallized pelletsfrom,sintering together.

Preparation of the reducing agent The limestone and coke or coal as thecase may be are dry ground together in the proper proportions as in anair-swept ball mill 16. The degree of neness of grinding is dictatedprimarily by the size of the oxide pellets to be reduced. Generallygrinding is through 30 to 100 mesh screen. With 1/2" pellets, thereducing agent is desirably ground to pass 60 mesh. After grinding thematerial is stored in a bin 17.

The proportions of limestone to coke or coal in the reducing agent aredetermined primarily by Equations l to 4, but also by the concentrationof carbon monoxide desired within the reducing furnace. While thelimestone may vary within wide limits, large excesses are to be avoidedsince additional heat is required to decompose the excess stone. As ageneral proposition, sufficient limestone is provided so that anadequate interfering phase exists within the furnace, sufficient CO2 isprovided, sulfur is substantially completely absorbed from the coke, andthe fusion point of the coke ash is adequately raised. Suicient carbonis always present to react completely with the CaCO3 decompositionproduct CO2 to convert the same to CO, and also to react completely withthe CO2 produced in the Fe2O3 reduction. An excess of carbon over theserequirements is preferably provided. Because of the dilferent ores to bereduced, differences in CaCOS content of the various limestones, as wellas the fixed carbon content of the coke or coal being employed, it isdifficult to lay down a weight ratio of limestone to coke for examplewhich will perform properly in all cases. By way of illustration, areducing agent containing about l to 11/2 parts by weight carbon perpart by weight CaCO3 performs well in the present process to reduce orecontaining about 70 percent Fe203. With bituminous coal, however,substantially more CaCO3 is required to help prevent coking. It issufficient to say that at least enough carbon is provided to completelyconvert CO2 produced in the process to CO.

The furnace charge 60 percent coke (85 percent fixed C) and 40 percentlimestone' (80 percent CaCOa).

This charge has provedy eminently satisfactory in the process of thepresentinvention, as has a charge employing a reducing agent containingsubstantially equal weights of coke and limestone. While carbon ispreferably present in excess as indicated earlier, a tentative practicallower iirriit for carbon as coke may be expressed: Coke about 30 percentof the weight of the pellets (70 percent Fe) plus about l0 percent ofthe weight of thc limestone.

The reduction operation the charge is fed from conveyor 19,simultaneously with a controlled amount of air and an oil-air or gas-airmixtur; which is ignited at burner 21. An induced draftflowingcocurrently with Vthe charge is created by exhaust fan 22. Thisco-curren't ow within the reducing zone is the reverse of blast furnaceand many previous operations for direct iron. Y

Referring to Fig. 2, it will be seen that enough air is introduced atthe charging end of the furnace to create an atmosphere above the chargewhich is fully oxidizing thereby to completely burn the fuel oil or gas.is thus a high release of heat at the charging end where it is mostrequired,V that is against the cold, unreduced charge, which rapidlyabsorbs heat and is not subject to sintering or sticking. As the chargereaches about 900 C., the limestone in intimate contact with the pelletsdecomposes forming carbon dioxide which is immediately reduced to carbonmonoxide within the charge which permeates the pellets reducing them toiron. The reaction rates increase due to the liberation of heat by theoxide reduction and become very rapid at l000 C. Success of the presentprocess is due primarily to the complete reducing condition producedwithin the charge. As lindicated in Fig. 2, the atmosphere surroundingthe pellets is substantially 100 percent carbon monoxide.

Large quantities of carbon dioxide liberated within the charge duringthe iron oxide reduction are also converted to carbon monoxide throughcontact with hot carbon. Infact, carbon-monoxide is evolved from thecharge and is pr'e'sent' in sui'cient excess in the atmosphere abovetl'ie bed -of material in the kiln that large quantities of the -sar'neare burned in the furnace without danger, since eoriditions within thecharge are fully reducing and there is an outward lliow of gas from thecharge. However, air introduced at the charging end is controlled sothat the atmosphere above the charge throughout a major "Y portion ofthe length of the furnace is reducing with respect to iron at 1000l050C. Generally, the ratio of COzCOz above the charge should not be allowedto fall below 2:1. As a practical matter it is only necessary to ensurethat the discharge gases entering hood 23 create alshort Vla'me thereinupon contact with air induced into 'the hood around the upper portion ofthe conical discharge end of kiln 20. The hot gas'es from the hood arepreferably employed in the pelletizing operation as indicated in Fig. l.

Temperature within the kiln is observed by means of a ipyro'irie'ter -24near the discharge end. 'If the pellets show incipient fusion of themetal, the temperature is too high, and it fm'ay be lowered byrestricting air introduced at the charging end or by reducing the flameat There 8 perature is desirably maintained safely below the maximum,and is preferably about 900 C.-l000 C.

The iron pellets and finely divided lime and ash issuing from theconical discharge end of kiln 20 are next cooled, preferably in a waterjacketed conveyor, illustrated as a screw conveyor 25. A minor portionof the reducing atmosphere from the kiln is directed to conveyor 25through line 26 and induced through the conveyor by a small blower 27.There is thus provided a non-oxidizing atmosphere around the metalpellets during cooling, so that the surface of the pellets is notoxidized.

Product separation The iron pellets and spent reducing agent powder arecollected in a hopper 28 at the discharge end of the cooling conveyor.This material may be conveyed to suitable screening or magneticseparating apparatus to free the pellets of lime, ash and any unreactedcarbon. However, I have found `that the metal pellets can be moreefficiently and completely separated from the spent reducing agentpowder and the `surface of the pellets can at the same time be cleanedby a novel air classifying process.

in accordance with this separation process, the pellets and powder areconveyed pneumatically from hopper 28 to a first or pellet separator 31in the form of an inverted cone, resembling an ordinary cyclone.Material enters the pellet separator 31 tangentially at reasonably highspeed induced by the suction of blower 32 and whirls around as indicatedin Fig. 3, with the pellets settling to thc base vof the separator concand discharging into storage bin 33. A strong updraft of air is providedwithin the pellet separator as well as at the pellet discharge endthereof by an air intake port 34 located in the upper portion of storagebin 33. By reason of the updraft, the powder is prevented from enteringthe storage bin, travelling instead centrally upward in separator 31 asindicated by the arrow in Fig. 3 and outwardly vthereof through overheadexhaust line 35. Through whirling action and ycontact with the morerapidly travelling particles of powder, the metal pellets areeffectively cleaned in the separator 31. They are then ground or meltedas their use dictates.

The pellets of substantially pure iron are more or less spongy accordingto the treatment given them before reduction. Pellets which have 'beenmade from pure ferrie oxide and flour binder and simply dried yield avery spongy product which disintegrates to an exceedingly tine powdersuitable for magnetic core production. On the other hand, pellets whichhave been prepared with onehalf percent by weight of alkaline oralkaline earth base and roasted above ll00 C. yield on reduction a lessspongy pellet which disintegrates to a relatively coarse powder rnoresuitable for the fabrication of mechanical parts. All types of pelletsmay be simply melted, or pressed and then melted if solid metal isrequired.

Exhaust line 35 of separator 31 is connected to a second or powderseparator 36, which may be a conventional cyclone separator. In thisapparatus, the powder is effectively collected and drops into storagebin 37, there being no induced updraft between storage bin andseparator.

The powder thus collected comprises burnt shaly lime together withcalcium sulde, some unused carbon and oxides other than calcium presentin the limestone. As indicated above the composition may be suitablewithout modification 'as a cement formulation. However, itis more likelythat slight adjustments of the metal oxide content of the powder will benecessary prior to conversion to cement. Calcination and clinkering ofthis residue to form cement is carried out in a conventional mannerrequiring temperatures over 300 C. higher than thoseencountered in thereduction operation. This heat is conveniently provided by the volatilegases from a coking operation conducted to provide the preferredcarbonaceous material for carrying out the present invention.

The total raw materials used in the present invention will vary with thetype of ore being reduced, and the process has been applied to a widevariety of ores ranging from high grade concentrates to pyrit-e cinderand blast furnace types. When operating for the production of high gradepowder from concentrates rating about 70 percent Fe, for each ton ofmetal pellets produced I have employed 1.43 tons of pellets one-halfinch in diameter, 0.6 ton of soft coke iines, 0.6 ton of shale limestone(both coke and stone through 60 mesh), and about 0.4 ton of fuel oil.Reduction was complete in two hours at 1000o C., approximately one-fourthe time required in a blast furnace. The pellets had the followinganalysis:

The present invention has been described employing a rotary kiln as thereduction furnace, and this is the preferred apparatus for carrying outthe process. However, the stationary tunnel type with continuous movingconveyor or vibratory hearth, as well as the Well known Herreshoffsuperimposed multiple hearth furnace may also Vbe employed with goodresults.

What is claimed and desired to be secured by Letters Patent is:

l. A continuous process for the reduction of iron oxide to iron inspongemetal form which comprises forming ore comprising iron oxide intosubstantially round pellets, heating said pellets under oxidizingconditions until the same are substantially fully oxidized, wherebysulfur is removed therefrom and said pellets are changed into a hard,porous crystalline state, mixing therewith a reducing agent in finelydivided form comprising limestone and a solid carbonaceous materialcapable of reducing carbon dioxide to carbon monoxide, said limestoneand its solid decomposition product serving as an interfering phasebetween said pellets during reduction, the quantity of carbonaceousmaterial in said reducing agent being at least sucient to reduce all ofthe carbon dioxide liberated by decomposition of said limestone as wellas that evolved in the iron oxide reduction to carbon monoxide,providing a reducing zone, charging said mixture of iron oxide pelletsand reducing agent to said zone and providing a bed of said mixturetherein, directly heating said mixture within said zone with anoxidizing condition at its charging end to a temperature suicient todecompose said limestone to lime and carbon dioxide, whereby at saidtemperature said carbon dioxide is reduced within the bed by the alsohot carbonaceous material to carbon monoxide which permeates saidpellets reducing the same to iron with the evolution of carbon dioxidewhich is likewise reduced by said hot carbonaceous material, theatmosphere above the bed being non-oxidizing with respect to iron at thetemperature within the furnace over the remaining length of the furnace,advancing said bed and atmosphere co-currently through said reducingzone to the discharge end thereof, and allowing said oxide reduction tocontinue to substantial completion therein, conducting the resultingiron pellets and spent reducing agent issuing from said reducing zone toa cooling zone, and separating the iron pellets from the finely dividedspent reducing agent after discharge from said cooling zone.

2. Process in accordance with claim 1, wherein the solid carbonaceousmaterial is selected from the group consisting of coke, anthracite, andbituminous coal.

3. Process for the reduction of iron oxide to sponge iron whichcomprises forming ore comprising iron oxide into substantially roundpellets, heating said pellets under oxidizing conditions until the sameare substantially fully oxidized, whereby sulfur is removed therefromand said pellets are changed into a hard, porous crystalline state,mixing therewith a reducing agent in finely divided form comprisinglimestone and a solid carbonaceous material capable of reducing carbondioxide to carbon monoxide, the limestone in said reducing agent and itsdecomposition product serving as an infusible interfering phase betweenpellets thereby preventing their sintering together, said carbonaceousmaterial containing at least suiiicient fixed carbon to'reduce all ofthe carbon dioxide produced by decomposition of the limestone as well asthat evolved in the iron oxide reduction to carbon monoxide, providing arotating kiln, charging said mixture of iron oxide pellets and reducingagent to said kiln and providing a bed of said mixture therein, heatingsaid mixture within said zone and under oxidizing conditions adjacentsaid charging end to at least about 900 C., whereby decomposition ofsaid limestone to lime and carbon dioxide within said bed is initiatedas well as reduction of the latter by the also hot carbonaceous materialto carbon monoxide which permeates said oxide pellets reducing the sameto iron with the evolution of carbon dioxide which is in part reduced tocarbon monoxide within and in contact with the said bed, the atmosphereabove said bed over substantially the remaining length thereof, beingnonoxidizing with respect to iron at bed temperature and increasingly sotoward the discharge end of the furnace, maintaining the temperature ofsaid bed between about 900 C. and about 1050 C., advancing said bed andsaid atmosphere co-currently through said reducing zone to the dischargeend thereof and allowing iron oxide reduction to continue to substantialcompletion, conducting the resulting iron pellets and spent reducingagent discharged from said reducing zone to a cooling zone, maintainingan atmosphere within said cooling zone which is non-oxidizing to theiron pellets introduced thereto, and after cooling, separating the ironpellets from the finely divided spent reducing agent.

4. Process according to claim 3, wherein the nonoxidizing atmospherewithin the cooling zone is a minor portion of the non-oxidizingatmosphere from the reducing zone.

5. A continuous process for the reduction of iron oxide to sponge ironwhich comprises forming ore comprising iron oxide into substantiallyround pellets, heating said pellets under oxidizing conditions until thesame are substantially fully oxidized, whereby sulfur is removedtherefrom and said pellets are changed into a hard, porous crystallinestate, mixing therewith a reducing agent in iinely divided formcomprising limestone and a solid carbonaceous material capable ofreducing carbon dioxide to carbon monoxide, said limestone andcarbonaceous material and their solid decomposition products serving asan interfering phase between pellets, thereby preventing sinteringtogether of the pellets in the process, the fixed carbon of saidcarbonaceous material present in the mixture of pellets and reducingagent being at least sufficient to reduce carbon dioxide produced bydecomposition of said limestone and by reduction of said iron oxide tocarbon monoxide, providing a rotating kiln, continuously charging saidmixture of iron oxide pellets and reducing agent thereto and providing agently agitated bed of the mixture therein, introducing a quantity ofair at said charging end thereby providing an oxidizing atmosphere atthe charging end of said zone, heating said mixture adjacent saidcharging end to at least about 900 C., whereby decomposition of saidlimestone to lime and carbon dioxide within said bed is initiated aswell as reduction of the latter by the also hot carbonaceous material tocarbon monoxide which permeates said oxide pellets reducing the same toiron with the evolution of carbon dioxide which is in part reduced tocarbon monoxide within and in contact with said bed, and whereby carbonmonoxide is evolved from said bed, allowing a portionl of said evolvedcarbon monoxide to burn to carbon dioxide above the bed whilemaintaining the atmosphere within said zone above the bed non-oxidizingwith respect to the hot iron being produced from a point adjacent thecharging end tothe discharge end of said reducing zone, advancing saidbed and non-oxidizing atmosphere co-currently through said zone at a bedtemperature between about 900 C. and about 1050" C. and allowing ironoxide reduction to continue to substantial completion, continuouslydischarging from said reducing zone the resulting iron pellets and spentreducing agent to a` cooling zone maintaining an atmosphere within saidcooling zone which is non-oxidizing to said iron pellets introducedthereto, and separating the iron pellets from the' finely divided spentreducing agent after discharge from saidcooling zone.

6. Process according. to claim 5, wherein the ratio of CO:CO2 attheatmospherev above the bed in the reducing zone ismaintained above about2:1.

7. Process according toclaim' 5, wherein the solid carbonaceous materialis anthracite coal.

8. Process according toclaim 5, wherein the solidy carbonaceous materialis coke.

9. Process according to claim 5, wherein thetixed carbon inv saidreducing agent isat least equal to the weight of calcium carbonatetherein.

10. Process according4 to claim'S, wherein the iron oxide pelletscomprise hematite andthe mixture charged to the reducing zone comprises100 parts by weight of said. pellets and between about 60 and about 80parts by weight 12 of reducing agent comprising carbon and calciumcarbonate in the' weight ratio of about 1 to 11/2 parts carbon per partcalcium carbonate.

ll. Process according to claim 5, wherein the limestone of saidreducing' agent is a' limestone of cement making characteristics,` andincluding the additional steps of adjusting the composition of saidfinely divided spent reducing agent separated from said iron pellets toa cement formulation, and continuously calcining the thus modifiedmaterial to cement.

References Cited in the tile of this patent UNITED STATES PATENTS OTHER-REFERENCES Proceedings of BlastV Furnace and Raw Materials, volume 4,1944', pages 58-59; A. I. M. E., 29 West 39th St., NewYork.

UNITED STATES PATENT OFFICE W CERTIFICATE 0F CRRECTION Patent No.,2,855,290 October '7 1958 Horace Freeman It is hereby certified 'thaterror appears in the printed specification of' the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column ll, line` 20, for "at the atmosphereu read ee in the atmosphereen Signed and sealed 'this 30th day of December 3.955*

SEAL) nest:

KARL Ho l AXLIIE ROBERT C. WATSON Attesting @flitser Commissioner ofPatents

1. A CONTINUOUS PROCESS FOR THE REDUCTION OF IRON OXIDE TO IRON INSPONGEMETAL FORM WHICH COMPRISES FORMING ORE COMPRISING IRON OXIDE INTOSUBSTANTIALLY ROUND PELLETS, HEATING SAID PELLETS UNDER OXIDIZINGCONDITIONS UNTIL THE SAME ARE SUBSTANTIALLY FULLY OXIDIZED, WHEREBYSULFUR IS REMOVED THEREFROM AND SAID PELLETS ARE CHANGED INTO A HARD,POROUS CRYSTALLINE STATE, MIXING THEREWITH A REDUCING AGENT IN FINELYDIVIDED FORM COMPRISING LIMESTONE AND A SOLID CARBONACEOUS MATERIALCAPABLE OF REDUCING CARBON DIOXIDE TO CARBON MONOXIDE, SAID LIMESTONEAND ITS SOLID DECOMPOSITION PRODUCT SERVING AS AN INTEFERRING PHASEBETWEEN SAID PELLETS DURING REDUCTION, THE QUANITY OF CARBONACEOUSMATERIAL IN SAID REDUCING AGENT BEING AT LEAST SUFFICIENT TO REDUCE ALLOF THE CARBON DIOXIDE LIBERATED BY DECOMPOSITION OF SAID LIMESTONE ASWELL AS THAT EVOLVED IN THE IRON OXIDE REDUCTION TO CARBON MONOXIDE,PROVIDING A REDUCING ZONE, CHARGING SAID MIXTURE OF IRON OXIDE PELLETSAND REDUCING AGENT TO SAID ZONE AND PROVIDING A BED OF SAID MIXTURETHEREIN, DIRECTLY HEATING SAID MIXTURE WITHIN SAID ZONE WITH ANAXIDIZING CONDITION AT ITS CHARGING END TO A TEMPERATURE SUFFICIENT TODECOMPOSE SAID LIMESTONE LIME AND CARBON DIOXIDE, WHEREBY AT SAIDTEMPERATURE SAID CARBON DIOXIDE IS REDUCED WITHIN THE BED